My Virginia ballot was mailed in and received a while back. Plenty of others have spelled out the reasons a conservative would vote for neither of the major candidates this time around, so I won’t belabor those points here.
I will, however, briefly note that a vote for a third party is not a vote for the other guy, either mathematically or tactically. In race where only two candidates have a shot at winning, you have three options — Candidate A, Candidate B, and neither. Voting for A instead of B actually shifts the spread by two votes, not just one, making the middle option a distinct choice with a different effect.
If a race is 5–3 without your vote and you pick one of the major candidates, you can make it either 6–3, a three-vote spread, or 5–4, a one-vote spread. Voting for someone else, by contrast, leaves it a two-vote spread. In addition, through your choice of a third-party candidate you can communicate to the major parties what kind of person they should run next time if they want your vote.